This invention is directed to the field of real-time color comparators which performs color comparison of sample objects to reference colors for the purpose of identification, sorting or matching.
Manufacturing and process automation sometimes require the determination of whether a colored sample matches that of a colored reference. For example, if the reference color represents the desired output characteristic of a continuous process (e.g., paint mixing, chemical reactions, baking), the real-time color comparator can be used as an endpoint detector for the process.
In the present invention use is made of spectral reflectance distributions of sample versus reference colors, that is, the colors per se are compared indirectly. In the present invention a reference color object and a sample object are similarly illuminated. Two optical paths are positioned to observe the reference object and the sample object; in the embodiment disclosed separate optical fibers are utilized, a reference fiber to observe the reference object and a sample fiber to observe the sample object. The outputs from the two fibers are directed onto a spectral dispersive element shown in the form of a concave diffraction grating that decomposes each light signal into its spectral constituents which are imaged on a photodetector array. Photodiodes in the array generate an analogue signal which represents the color signature of the object. The color signature from the reference and the color signature from the sample are compared.